What does code P21B4 mean?

Q: What does code P21B4 mean?

NOx Adsorber Over Temperature (Bank 1). P21B4 indicates that the powertrain control module has detected an excessively high temperature at the NOx adsorber catalyst on Bank 1, which is the side of the engine containing cylinder number one. The computer monitors this temperature using sensors before and after the adsorber, and it sets the code when the calculated or measured temperature exceeds a calibrated threshold that could damage the catalyst.

DTC codes / P21xx · Fuel and air metering / P21B4

P21B4NOx Adsorber Over Temperature (Bank 1)

P21B4 indicates that the powertrain control module has detected an excessively high temperature at the NOx adsorber catalyst on Bank 1, which is the side of the engine containing cylinder number one. The computer monitors this temperature using sensors before and after the adsorber, and it sets the code when the calculated or measured temperature exceeds a calibrated threshold that could damage the catalyst.

SystemPowertrain

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaFuel and air metering

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.